1. Field of the Invention
The present invention relates in general to air cleaning devices for use in a motor vehicle, and more particularly to air cleaning devices of a type which cleans the surrounding air fed to a passenger compartment of the motor vehicle from the outside of the vehicle.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional air cleaning device of the above-mentioned type will be described with reference to FIG. 29 of the accompanying drawings.
In FIG. 29 , the conventional air cleaning device is shown, which is mounted in a front part of a motor vehicle. That is, the air cleaning device comprises generally an air box 1 which is mounted beneath a cowl top 2 of the vehicle. The cowl top 2 is formed with an air intake opening 3 through which the atmospheric air is introduced into the air box 1. Within the air box 1, there is installed a cowl duct 5 through which the interior of the air box 1 is connected with an air intake case 4. Although not shown in the drawing, the air intake case 4 is led to a passenger compartment of the vehicle through suitable guide ducts. An air filter element 6 constructed of pleated paper is disposed on the cowl duct 5 and an electric air blower 7 is mounted in the air intake case 4. Upon energization of the air blower 7, the atmospheric air in the air box 1 is forced to pass through the air filter 6 and the air thus cleaned is led to the passenger compartment through the guide ducts.
However, due to its inherent construction, the above-mentioned air cleaning device has the following drawbacks and weak points.
First, when the air filter 6 becomes severely blocked or clogged with arrested dust due to long use or the like, the amount of fresh air fed to the passenger compartment is considerably reduced. In particular, in winter, a temporary blocking of the air filter 6 tends to occur due to freezing of moisture in the filter 6. In this case, the passenger compartment is given substantially no fresh air through the air cleaning device. Furthermore, a marked load is applied to the electric air blower 7.
Second, due to the nature of the pleated paper by which the air filter 6 is made, the conventional air cleaning device exhibits a marked air flow resistance. Furthermore, the shape of air flow passage defined in the device is given little thought, which promotes the marked air flow resistance of the device. These induce that high power and thus expensive air blower 7 is necessary for feeding the passenger compartment with a satisfied amount of clean air.
Third, it is very difficult to check and change the air filter element 6. In fact, in the conventional device, for such maintenance, it is necessary to dismantle the entire of the cowl top 2 from the vehicle body.
Fourth, due to the nature of the pleated paper by which the air filter 6 is made, the filter 6 fails to catch very fine particles.